1977.5 400 2bbl C6 no air. My truck has been running fine until today.

Turn the key and nothing or just some solenoid chatter with the lights on but kinda dim or they don't come on at all. Hmmmm... Ok, Clean battery cable connections check the solenoid bolts are tight the ground strap from engine to the cab is there and in decent shape. The starter itself is about two years old from Napa. Still no luck. Allright, the battery is five years old Farm Fleet pull the caps and discover all the cells are about dry add some water put the charger on it.

Still no luck but a new observation when I turn on the parking lights I see power with a test light at the negative battery post none at the positive post. Parking light switch in the off position and I have power at the positive post not at the negative post.

The voltage regulator looks to perhaps be the original. Suggestions appreciated.

 

I don't follow what you mean by power at the negative post, but none at the positive post. Please explain your setup and what you have connected specifically. Honestly, it sounds like a dead battery; checking with a multimeter would tell you right away. Relay chatter means too low of a voltage is available at the solenoid, so if you've already checked the battery cables, I'd direct your attention to the battery once more.